i'm so confused...

and i come here seeking enlightenment. this movie was just... wow, i don't even have a word for it. if i hadn't read the plot summary on amazon, i would have had NO IDEA what was going on.
so... what was with the goat? why was he growling and... well, standing menacingly in a corner? did the father made him demonic, or the grandfather?
why was there a random flashback sequence at the end? and why did the reverend invite the drug addicts to his farm?
and where did the zombies come from? i know this is a lot of questions so... i guess what i'd really like is if someone who understood it could write a plot summary explaining all these seemingly random events..

"elmo went to the wrong fundraiser"